Learner differences in the field of second language acquisition could be studied from different perspectives. The reason lies in the fact that each individual is unique considering cognitive, affective and socio-cultural factors. One of the considerations in the field of individual differences is the role of attention and its different degrees in the process of language learning. This study focuses on the meaning of attention with respect to its definitions and its significant role in SLA. It discusses briefly three main approaches to the definition of attention in SLA theories namely Schmidt’ noticing hypothesis, Robinson model and Tomlin and Villa’s functional model of input processing. It also draws the interest of teachers to the differences exist in the field of SLA considering the role of attention in interlanguage. It concludes that teachers should recognize that not all learners have the same level of attention which is an influential factor in the process of second language learning.